Joint whole exome sequencing and linkage analysis in a multigenerational family segregating Type 1 Diabetes

Backround: Type 1 diabetes (T1D) is a complex autoimmune disease with a strong familial segregation. On the other hand, the recent and rapid increase in incidence is a proof of the importance of environmental factor in the etiology of disease. Linkage and Genome-wide association studies had revealed almost 60 loci associated with the risk of T1D, explaining about 80% of the total heritability, mostly due to HLA locus. However, many familial T1D cases remains unexplained. Objective: To identify rare variants contributing to T1D susceptibility, we studied a Sardinian family with 9 individuals affected across 3 generations. Methods: We performed exome sequencing in 3 affected members and a healthy individual. In addition, all samples were extensively genotyped using Illumina OmniExpress beadchips for about 750K SNPs. A combined linkage analysis was carried out. Results: This combined approach identified three variants predicted to be damaging that are very rare in the general population (frequency <1%) and that are likely causing the disease.